1. Field of the Invention
The present invention relates to a brushless motor control apparatus and to a brushless motor control method for controlling a brushless motor which includes a rotor of the permanent magnet type.
Priority is claimed on Japanese Patent Application No. 2003-386569, filed Nov. 17, 2003, the content of which is incorporated herein by reference.
2. Description of the Related Art
In the past, for control of a brushless motor, as a method of measuring the rotor angle with good accuracy without employing any position measurement sensor for performing measurement of the position of the rotor, there has, for example, been a method of doing so by applying, to a voltage command value for controlling the motor rotation, a higher harmonic voltage such that the rotor is not additionally rotated thereby. In concrete terms, there is a per se known method of, along with measuring the rotor angle which gives the position of the rotor from the motor electrical current that flows in each phase of the motor due to the harmonic voltage which has been applied to the voltage command value, also applying a voltage for magnetic pole detection in the direction of the magnetic field and thereby discriminating the orientation of the magnetic poles of the rotor. In this case, for discriminating the orientation of the magnetic poles of the rotor, since, when an electrical current flows in the direction of the magnetic field and has generated a magnetic field, the state of the motor electrical current which flows in each phase of the motor changes with the state of saturation when the direction of the magnetic field which is generated by the electrical current and the direction of the magnetic field which is generated by the magnet are the same, and with the state of non saturation when the direction of the magnetic field which is generated by the electrical current and the direction of the magnetic field which is generated by the magnet being opposite, accordingly it is possible to decide upon the orientation of the magnetic poles of the rotor by discriminating these changes (for example, refer to Unexamined Japanese Patent Application, First Publication Nos. 2002-171798 and 2002-320398).
Thus, with a control device for a brushless motor as described in JP 2002-320398, in order to cause the motor to rotate with the desired torque or speed of rotation, control is performed so as to bring the fed-back motor electrical current (the actual electrical current) to approach to the electrical current command value for controlling the rotation of the motor. In concrete terms, as shown in the following Equation (1) and Equation (2), voltage command values Vd′ and Vq′ in order to control the rotation of the motor by PI (proportional integral) control are calculated, based upon the differences Iderr and Iqerr between the electrical current command value and the motor electrical current (the actual electrical current).Vd′=Kp(Iderr)+Ki∫(Iderr)dt  (1)Vq′=Kp(Iqerr)+Ki∫(Iqerr)dt  (2)
Moreover, in Equations (1) and (2), Kp is the proportional gain, and Ki is the integral gain.
However, with this type of control device, while it is possible to rotate the motor at the desired torque or rotational speed, when starting driving of the motor for the first time (upon initial starting), there is the problem that it takes some time before the orientation of the magnetic poles of the rotor is discriminated by the magnetic pole discrimination procedure. In concrete terms, when PI control is performed for calculating the voltage command value Vq′, the time constant until the voltage command value Vq′ is calculated is long, and the peak electrical current in both the positive and negative directions of the motor electrical current (the actual electrical current) is not stable in the short term. Due to this, the magnetic field which is generated by this electrical current is also not stable, and accordingly it takes a relatively long time before it is possible to discriminate the orientation of the magnetic poles of the rotor, since it is not possible to perform the magnetic pole discrimination procedure accurately until the magnetic field has stabilized.